1. Field of the Invention
The present invention relates to mobile radio communications, and more particularly to a delay adjustment technique for a radio base station apparatus which communicates with mobile communication terminal apparatuses.
2. Description of the Related Art
By taking TCP (Transmission Control Protocol) communication between a radio base station apparatus and a mobile communication terminal apparatus as an example, location service will be described. In TCP communication, RTT (Round Trip Time) is determined based on the following information (a) and (b);
(a) Arrival time of a down link signal transmitted from a radio base station apparatus to a mobile communication terminal apparatus.
(b) Arrival time of an ACK (Acknowledgement) signal of an up link signal transmitted from a mobile communication terminal apparatus to a radio base station apparatus. Based on the determined RTT, retransmission timer value for ACK is determined, or location identification is performed.
RTT is only the period of time for an IP packet to travel back to forth between TCP end points. RTT doesn't include the delay that the radio base station apparatus cause within its circuits. Any delay adjustment based on RTT doesn't exactly adjust the delay introduced by radio base station apparatus circuits
Thus, the delay that the radio base station apparatus circuits introduce also must be adjusted particularly. The delay adjustment for the radio base station apparatus is made based on the delay time observed within the radio base station apparatus.
Conventionally, the delay of the radio base station apparatus is usually adjusted using tester, etc. for transmitter with following procedures;                Measurement of the deviation of delay time.        Adjustment a delay adjuster circuit of the radio base station apparatus.Above conventional way of delay adjustment is performed manually. And measuring instrument or device is required, thus posing a problem.        
Moreover conventional way of delay adjustment must be performed when the radio station apparatus is not in service;                Installation time of the radio base station apparatus.        Maintenance time of the radio base station apparatus for readjustment the change of delay due to aging.Thus causing a further problem.        
Several methods have been hitherto proposed to solve the problems.
For example, in Japanese Patent Laid-Open No. 2003-258694, there is disclosed a method for delay adjustment. Specifically, the changing patterns of amplitude level are compared between the input and output signal waves of the radio apparatus to thereby detect a corresponding timing-difference. Then, a control is performed so that the radio apparatuses of a diversity configuration have the same timing difference. In the radio apparatus according to the above invention, this control eliminates the difference of transmission delay time between the radio apparatuses of a diversity configuration.
In Japanese Patent Laid-Open No. 2002-374193, there is disclosed a delay control technique. Specifically, in a radio apparatus according to the above invention, a transmit diversity delay control is performed by employing TSTD (Time Switch Transmit Diversity) including system 0 with a transmitting and receiving function and system 1 with a transmitting and receiving function.
In Japanese Patent Laid-Open No. 2003-158774, there is disclosed a W-CDMA radio base station and a delay time difference elimination method in which the delay time difference between transmitter system 0 and transmitter system 1 of a transmit diversity configuration is automatically corrected.
In Japanese Patent Laid-Open No. 9-214467, there is disclosed a configuration in which the measurement and adjustment of propagation delay are periodically performed during a idle time in which a call is not made; during call, a closed-loop control for delay equalization is performed by using CDMA transmission of a subscriber unit to thereby compensate for small fluctuations of delay time.
However, in a system in which the same frequency is used by plural users, such as CDMA (Code Division Multiple Access), a scheme is used to multiplex plural signals with respective codes to thereby use frequency more efficiently. In the system in which such scheme is used, the amplitude change of outputted signals is rapid and sharp, making it difficult to accurately compare the change patterns of, amplitude level between the two signal waves. In addition, transmission power in CDMA communication has a large peak level; therefore, to reduce distortions introduced in high-power amplifier device of analog stage, signal level is limited typically in digital stage before the signal is converted from digital signal into analog signal and fed into analog stage. Due to the amplitude limitation processing, the peak value is rounded up. Consequently, it can be difficult to identify the peak point.